A four stroke engine having at least two cylinders spaced vertically relative to each other. Each cylinder includes a cylinder body having a cylinder bore extending generally horizontally. Plurality of air intake ducts are provided for connecting a common plenum chamber and respective air intake passages which extends to respective combustion chambers. Each of the air intake ducts has a generally straight section extending generally horizontally and parallel to each other. The distance between the straight sections is less than the distance between the axes of the cylinder bores. Also, in another feature, throttle body means are interposed between duct members, which are upstream components of the air intake ducts, and the intake passages for controlling the flow of air to the combustion chambers.